A wireless communication network is a large distributed system for receiving information (signal) and transmitting the information to a destination. Use of radio frequency bands of the electromagnetic spectrum is regulated by governments in most countries, in a Spectrum Management process known as frequency allocation or spectrum allocation. Since radio propagation does not stop at national boundaries, governments have sought to harmonize the allocation of radio frequency bands and their standardization. On a global level, there are several government organizations that work together to determine the standards for frequency allocation, such as, the International Telecommunication Union (ITU), the European Conference of Postal and Telecommunication Administration (CEPT), and the inter-American Telecommunication Commission (CITEL). The Federal Communication Commission (FCC) is an independent agency of the United States Government created to regulate interstate communications by radio, television, wire, satellite, and cable in all 50 states, the District of Colombia, and the U.S. territories.
A radio spectrum is the range of frequencies that is used for wireless applications, such as broadcast television and radio, cell phone, satellite radio and television, wireless computer networks, Bluetooth, Global Positioning Services, police dispatch, and many other general and specialized applications that we use every day. Usually, it is difficult for these applications to utilize the same frequencies simultaneously. For example, if a local television station uses the same frequency as a cell phone, then the cell phone would not work very well due to interference from the television station, or the television picture would be fuzzy due to interference from the cell phone, or perhaps both. Therefore, to avoid such interference, the radio spectrum is carved up into different portions, and each portion is allocated to one or more services that, generally speaking, may be able to co-exist with each other.
The use of the radio spectrum is at an all-time high due to the increase use of mobile voice and data. As a result, the demand for additions, modifications, and waivers to existing spectrum allocation is also growing. As such, the FCC decided to create the Citizen Broadband Radio Service (CBRS) in the 3.5 GHz band, making 150 MHz available for mobile broadband and other commercial services. The CBRS includes the band of spectrum from 3550 MHz to 3700 MHz. To date, only the 3650-3700 MHz portion of the band has been accessible to non-federal operators using a non-exclusive licensing process. The 150 MHz that the CBRS is opening up for use, employs a 3-tier access/licensing model. The 3-tier access includes incumbent access, priority access licenses (PAL), and general authorized access (GAA).
By increasing the spectrum band usage in a wireless communication system, it may become difficult to identify if a transmitter signal is being interfered with by another transmitter. In addition, it may also be difficult to identify which transmitter is causing the interference. Direction finding (DF) antennas are often used to identify rogue transmitters. DF or radio direction finding (RDF) is the measurement of the direction from which a received signal was transmitted. DF combines the direction information from two or more suitably spaced receivers (or a single mobile receiver); the source of a transmission may be located via triangulation. In some examples, RD is used in navigation of ships and aircrafts, to locate emergency transmitters for search and rescue, for tracking wildlife, and to locate illegal or interfering transmitters. DF antennas are difficult to use for several reasons, including but not limited to, the fact that the direction that a signal arrives at a certain location does not always indicate the location of the transmitter. For example, the signal of the transmitter may have bounced off a physical structure and tracing the signal back from the victim transmitter may lead back to the physical structure.